1. Field of the Invention
The present invention relates to a porous sepiolite and a process for producing the same. The invention specifically is concerned with a porous sepiolite which has an improved resistance to water, an improved resistance to thermal shock and a large specific surface area, and with a process for producing the same. This invention also relates to a catalyst composition for deodorization in which a catalyst component is supported on such a porous sepiolite.
2. Description of the Prior Art
Sepiolite is a clay which has tunnels therein along its fibers. Sepiolite is a unique mineral in that it is very soft and has a large adsorption capacity like zeolite. Sepiolite keeps suspension in water like bentonite and has properties of thixotropy and plasticity. In addition, it can be set like kaolinite when kneaded with water and dried or calcined.
An attempt to form sepiolite into a porous molded article has been made in Japanese Patent Publication No. 31085/80.
The above Publication discloses a sepiolite molded article for use in a heat insulator, an acoustic material, an adsorbent and a catalyst support. The specific surface area of the article is no less than 200 m.sup.2 /g. The pores of 74 angstroms or larger have a specific surface area of 100 m.sup.2 /g or more and have a pore volume of 0.5-1.0 cc/g. The ratio of the pore volume of pores having a pore diameter of 200-600 angstroms to that of pores having a pore diameter of 74 angstroms or larger is not less than 60%.
The Publication No. 31085/80 discloses a process for production of a molded sepiolite which comprises the following steps:
(a) grinding sepiolite and adding water thereto to make a moisture-conditioning; PA1 (b) sufficiently kneading the resulting sepiolite; and PA1 (c) molding the kneaded sepiolite and calcining the resultant.
The above Publication discloses an embodiment wherein the temperature of calcination is in the range of 300.degree.-500.degree. C. Example 3 in the publication states that aluminum nitrate was added to sepiolite to effect 3% of an aluminum metal ratio and the calcination was conducted at a temperature of 800.degree. C. to thereby produce a sepiolite having some less pore volume, but a larger specific surface area and a highly improved crushing strength.
The resultant produced in the above manner and calcined at a temperature in the range of 300.degree.-500.degree. C. has the problem on water-resistance that it is deflocculated or peptized when it is immersed in water. When sepiolite per se is fired at a temperature of 800.degree. C. or higher, the resultant is transformed into steatite, and the strength thereof is decreased, but the brittleness thereof is increased.
Japanese Patent Publication No. 18321/84 mentions that the pore volume and specific surface area were increased remarkably by an acid treatment of natural sepiolite.
The above Japanese Patent Publication discloses that the chemical reaction of natural sepiolite with a magnesium-eliminating agent to release a magnesium skelton from the sepiolite yields denatured sepiolite with a remarkably high porosity in comparison with natural sepiolite. The publication also mentions that such a sepiolite is useful as a catalyst for hydrogenation of heavy oil, especially for hydrodemetalization of heavy oil. The Publication, however, describes no information of pores having a pore diameter of 50 angstroms or less pores, which are particularly effective for adsorption. The publication does not suggest any porous sepiolite in which the pores having a pore diameter of 50 angstroms or less have a specific surface area in the range of 40 to 200 m.sup.2 /g and in which no less than 20% of the total surface of the sepiolite is occupied by the pores having a pore diameter of 50 angstroms or less and wherein the pore distribution curve of the sepiolite has a main peak at a pore diameter of no more than 50 angstroms. The publication does not suggest any adsorptive decomposition catalysts which take advantage of such excellent adsorption activities, either.